Many fabrics have been developed in the past for use as disposable operating room gowns, surgical drapes and wraps for medical components. These fabrics which must be fluid repellent and themselves sterilizable are used to maintain sterility by providing a barrier to contamination; and in the case of fabrics used for operating gowns, it is important that the fabric is breathable and possess sufficient drape for comfort. U.S. Pat. No. 4,501,792 discloses a breathable, repellent, soft fabric with enhanced drape and enhanced frictional properties. This fabric comprises cellulosic fibers and polymeric fibers, the fabric comprising rudimentary discontinuous rows of entangled cellulosic fibers alternating with rudimentary discontinuous rows of loosely entangled polymer fibers, the rows extending in the machine direction and the fabric having a surface comprising predominately entangled cellulosic fibers and a surface comprising predominately entangled polymeric fibers, at least the cellulosic fibers being subject to a repellent treatment. The repellency of the gown of U.S. Pat. No. 4,501,792 is accomplished by finishing the fabric with a suitable repellent such as a fluorochemical. The fluorochemical molecules interact with the pulp layer of the fabric and subsequent high temperature curing allows the fluorochemical "tails" to orient themselves away from the pulp fiber to produce a low surface energy barrier to aqueous fluids. However, the porosity of the base substrate is a primary factor in achieving a superior degree of repellency. The more porous the substrate is, the more the repellency rate decreases (even if finished with a superior fluorochemical treatment). The fabric of U.S. Pat. No. 4,501,792 is composed of a core of entangled polymer, preferably polyester, which is about 40% by weight, with a pulp tissue layer that is about 60% by weight entangled into the polyester core. The top pulp layer of the fabric of U.S. Pat. No. 4,501,792 is composed of individual pulp fibers and fines that are intermeshed and held together mainly by hydrogen bonding. The entangling process by means of which said fabric is made leaves the fabric with certain pulp-poor areas as well as with fine holes. Aqueous fluids penetrate the fabric more readily at the defect sites than at the areas where the pulp layer is dense and uniform. Accordingly, the fabric of U.S. Pat. No. 4,501,792 possess a rather high air-porosity and thus a relatively low repellency rating. In accordance with the present invention, there is provided a method which improves said repellency rating.
Defensive Publication No. 17060 discloses a two-sided laminar fabric formed by uniting a web of synthetic fibers with paper sheet by mechanical entangling, fluid entanglement and/or bonding. A DuPont fabric sold under the name "Fabric 450 TM" comprises an entangled fabric of polymeric and wood pulp fibers containing alternating rows of wood pulp and polymeric fibers with a thin veneer of wood pulp on one surface thereof. The coating process of the present invention may be utilized in order to improve the repellency rating thereof.
The present invention describes the improvement of repellent properties by reducing the porosity of a nonwoven base fabric by depositing a second layer of pulp onto the surface of the fabric utilizing a dilute pulp/water slurry. The second ply of pulp which is applied onto the pulp side of the fabric serves to fill in the holes in the pulp-poor areas that were created during the entangling process. The repellent properties of the two-ply pulp fabric improves hydrostatic head, drop test and impact spray rating in comparison to a similar untreated fabric.
Although the technology producing a pulp sheet by applying multiple layers of pulp on top of each other has existed in the paper making industry for many years, the present concept of forming a second layer, or multiple layers of pulp on the surface of an entangled nonwoven fabric has not been taught in the art.
A number of patents disclose processes for making pulp coated fabrics by depositing a thin layer or coating of wet paper pulp onto and into various fabrics in such a way that the paper pulp becomes a permanent and substantially integral part of the finished material. An example thereof is U.S. Pat. No. 1,854,414. Other patents relating to similar subject matter are U.S. Pat. No. 3,661,700; U.S. Pat. No. 2,913,365; and U.S. Pat. No. 1,782,785. However, none of said patents disclose an inital cross directional stretching of the fabric before the pulp layer is deposited thereon; which step is an essential and unobvious feature of the present invention. This initial cross-stretching step brings bout an expansion of the pores of the fabric which would be expected by a skilled person, to actually reduce the internal bond of the fabric. It has been found, however, in accordance with the present invention, that this cross-stretching step very surprisingly improves the Internal Bond of the resultant fabric as compared to unstretched fabric coated in the same manner.